Automobile air conditioning compressor superheat safety and ambient switch

ABSTRACT

In preferred form, a combination ambient temperature sensing switch and refrigerant superheat temperature responsive switch for an automobile air conditioning system having an electromagnetic clutch for transmitting engine rotation to a refrigerant compressor. The ambient temperature sensing portion of the switch is connected between the automobile battery and the coil of the clutch for energizing the coil whenever ambient temperatures are above a predetermined level. The refrigerant temperature responsive portion of the switch is connected between the battery and a fuse in short-circuit relation to the clutch coil to cause the fuse to blow in response to a predetermined maximum refrigerant temperature which closes the switch. A thermistor in circuit with the refrigerant temperature responsive switch delays the short circuiting of the clutch coil to prevent immediate blowing the the fuse.

United States Patent 7 Jacobs [54] AUTOMOBILE AIR CONDITIONINGCOMPRESSOR SUPERHEAT SAFETY AND AMBIENT SWITCH [72] Inventor: James W.Jacobs, Dayton, Ohio [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Aug. 6, 1971 [21] Appl. No.: 169,775

[52] 0.8. CI. ..62/158, 62/209, 62/228, 62/323 [51] Int. Cl ..F25b 27/00[58] Field of Search ..62/208, 209, 213, 217, 228, 62/323, 158

[56] References Cited UNITED STATES PATENTS 2,978,879 4/1961 Heidorn..62/323 2,981,076 4/1961 Gaugler ..62/323 3,047,696 7/1962 Heidom..62/209 Primary Examiner-Meyer Perlin Attorney-W. S. Pettigrew et a1.

[5 7] ABSTRACT In preferred form, a combination ambient temperaturesensing switch and refrigerant superheat temperature responsive switchfor an automobile air conditioning system having an electromagneticclutch for transmitting engine rotation to a refrigerant compressor. Theambient temperature sensing portion of the switch is connected betweenthe automobile battery and the coil of the clutch for energizing thecoil whenever ambient temperatures are above a predetermined level. Therefrigerant temperature responsive portion of the switch is connectedbetween the battery and a fuse in short-circuit relation to the clutchcoil to cause the fuse to blow in response to a predetermined maximumrefrigerant temperature which closes the switch.

A thermistor in circuit with the refrigerant temperature responsiveswitch delays the short circuiting of the clutch coil to preventimmediate blowing the the fuse.

2 Claims, 2 Drawing Figures AUTOMOBILE AIR CONDITIONING COMPRESSORSUPERIIEAT SAFETY AND AMBIENT SWITCH This invention relates to anautomobile air conditioning system and more particularly to acombination ambient temperature responsive control for energization ofan electromagnetic clutch above a predetermined ambient temperature anda refrigerant temperature responsive switch to de-energize the clutchwhen refrigerant temperatures exceed a predetermined level.

Automobile air conditioning systems commonly utilize a refrigerantcompressor driven by the automobile engine through an electromagneticclutch with a coil. It is undesirable to operate the air conditioningsystem below a predetermined ambient temperature range of approximately30 35 F. Operation below this temperature range will cause frost to formon the evaporator and block air flow therethrough. A portion of thepresent air conditioning switch assembly senses ambient temperatures andcloses above the 30 35 F. 6

range to energize the clutch coil and activate the air conditioningsystem when the automobile engine is running.

When the refrigerant charge level within the air conditioning systemfalls below a predetermined quantity which may be insufficient forpropercompressor cooling and lubrication, it is desirable to deactivate thecompressor until the charge level is replenished. Operation with aninsufficient charge level causes the refrigerant temperature in thesuction line between the evaporator and the intake of the compressor tobe increased above a predetermined level. This is partially becausethere is insufficient flow of refrigerant through the evaporator whichcauses refrigerant in the evaporator to become superheated by the heatinput to the evaporator. Superheat of refrigerant is a measure of thetemperature of refrigerant above its boiling point at a given pressure.

The present combination switch assembly includes a refrigeranttemperature responsive and a pressure responsive switch portion in heattransfer contact with refrigerant in the inlet of the compressor whichcloses in response to a predetermined high refrigerant temperature or apredetermined low refrigerant pressure. When the refrigerant temperatureresponsive switch portion closes, the compressors clutch coil is shortedby the switch and a fuse in circuit withv the automobile battery and theswitch is blown to render the compressor inoperative. A time delayingthermistor in circuit with the refrigerant temperature responsive switchportion prevents deactivation of the air conditioning system when highinlet temperatures of the compressor are encountered temporarily due toan operative cause such as rapid acceleration of the automobile ratherthan a low charge level.

Therefore, an object of the invention is to provide a combinationambient temperature responsive switch for energizing a compressor clutchcoil above a predetermined minimum ambient temperature and a refrigeranttemperature and pressure responsive switch which closes to deactivatethe compressor clutch coil in response to a predetermined maximumrefrigerant temperature level in the compressor inlet and in response toa predetermined low refrigerant pressure.

A further object of the invention is to provide a combination ambienttemperature responsive switch for energizing a compressor clutch coilabove a predetermined minimum ambient temperature and a refrigeranttemperature 'and pressure responsive switch which closes in response toa predetermined high refrigerant temperature in the compressors inletand a predetermined low pressure of refrigerant to short the compressorclutch coil and resultantly blow a fuse to render the air conditioningsystem inoperative until the fuse is replaced and the refrigerant chargelevel is replenished.

Further objects and advantages of the present invention will be apparentfrom the following detailed description, reference being hadto theaccompanying drawings in which a preferred embodiment of the inventionis clearly shown.

IN THE DRAWINGS FIG. 1 is a diagrammatic view of an automobile airconditioning system including the combination switch assembly; and pFIG. 2 is an enlarged sectioned view of the combination switch assemblyshown in FIG. 1.

In FIG. I of the drawings, an air conditioning system is shown includinga compressor 10, a condenser 12, a drier-receiver assembly vl4, anexpansion valve 16, an evaporator 18, and a suction throttling valve 20.These are all known elements used in automobile air conditioningsystems. The compressor 10 is connected in refrigerant flow relation tothe condenser 12 by a high' pressure conduit or a line 22. Theevaporator 18 and throttling valve 20 are connected in refrigerant flowrelation to compressor 10 by a suction conduit or line 24. A refrigerantcharged temperature bulb 26 and tube 28 sense evaporator outlettemperature to open and close the expansion valve 16.

The compressor 10 is rotated by the automobiles internal combustionengine (not shown) through an electromagnetic clutch 30 whenever theclutch coil 32 is energized. Electric power is applied to the coil 32 bya battery 34 through a conductor 36, a compressor protector fuse 38 anda conductor 40. Theconductor 40 extends to a terminal 42 of thecombination ambient temperature sensing and refrigerant temperaturesensing switch assembly 44. A conductor 46 extends from a secondterminal 48 of the switch assembly 44 to the coil 32. The coil 32 andbattery 34 are grounded respectively by conductors 50 and 52. An on-offswitch 54 is manually operated by the automobile driver to activate theair conditioning system when desirable.

The combination ambient sensing and refrigerant temperature sensingswitch assembly 44 is shown in more detail in FIG. 2. A cylindricalhousing portion 56 is supported within a bore 58 in the end 60 of thecompressor 10. An O-ring type seal 62 prevents fluid leakage between themember 56 and the end 60. A cover housing member 64 is threadablysecured to the housing 56 and supports terminals 42 and 48 therein. Themember 64 is molded of an insulation type material.

The terminal 42 projects through the interior 66 of housing 64 andsupports a contact 68 centrally within the interior 66. A contact arm 70extends from the other terminal 48 into the interior 66 and supports acontact 72 normally spaced from contact 68 but shown in its closedposition in FIG. 2. The contact 72 is moved to its closed position bythe expansion of a sealed belthreaded member 80 in a bushing 82 in covermember 64.:A passage 84 and tube 86 lead to the interior 88 of thecasing 74. The interior 88 is evacuated and subsequently filled withrefrigerant before the end of tube 86is crimped and brazed at 90 to sealthe casing. A pad 92 supported upon the movable disc 78 engages one faceof contact 72 and moves the contact against the adjacent contact 68vwhen the ambient temperature sensing switch closes in response toincreasing temperatures sensed by tube 86 which causes expansion ofcasing 74. The contacts 68 and 72 may be set to close at a desirableambient temperature of between 30 and 35 F. byturning the threadedmember 80 within bushing 82 to calibrate the ambient temperature sensingswitch portion.

As previously mentioned, the assembly 44 also includes a refrigeranttemperature responsive switch portion adapted to close when therefrigerant temperature in the compressor inlet or suction cavity 94exceeds a predetermined maximum temperature which corresponds to anundesirably low refrigerant chargelevel within the system. A fixedcontact 96 is mounted on the end of a support 98 within the interior ofhousing 56. The contact 96'and post 98 are insulated from housing 56 bya glass seal 100. The contact 96 is electrically connected through postsupport-98 and a connector button 102 to one end of a thermistor 104.The other end of the thermistor 104 is connected to and supported by thecontact 68 which is in the electric circuit with the fuse 38 and battery34. A bellows-like sealed casing 106 is supported in spaced relation tocontact 96 by a member 108 threadably secured to housing 56 within thesuction cavity 94. The casing 106 includes two spaced circular discs110,112 joined together at their peripheral edges and enclosing. aninterior 114. A passage 116 in member 108 and a tube 118 are used toevacuate the interior 114 and fill it with refrigerant before end 119 iscrimped and brazed together to seal the casing 106. A movable contact120 is supported on disc 112 and spaced from contact 96 when therefrigerant temperature sensing portion of the'switch assembly 44 isopen asshown in FIG. 2. Ports 122in member 108 permit the circulation ofrefrigerant from the suction cavity 94 around the casing 106. Thus, thecasing 106 responds to changes in refrigerant pressure from the suctioncavity 94 as well as changes in temperature. The glass seal 100 preventsrefrigerant from entering interior 66. I

When the refrigerant level within the system falls below a predeterminedlevel, it has been observed that the temperature of refrigerant in thesuction cavity 94 increases greatly and its pressure also decreases.This increased temperature .or decreased pressure causes enclosedrefrigerant within interior 114 of the casing 106 to expand andeventually to engage contacts 96 and .120. This completes a circuit fromthe battery 34 through the fuse 38, terminal 42, thermistor 104 and thehousing 56 to ground. After the. closing of contacts 96 and 120,.thethermistor 104 initially has a relatively high resistance but after abrief time delay of about one or two minutes, its resistance falls and alow resistance circuit is completed which bypasses the coil 32 causing alarge current to flow through the fuse 38. This large current blows thefuse 38and deactivates the compressor 10.

A refrigerant used in the aforementioned air conditioning system isdichlorodifluoromethane with the chemical formula CC1,F commonlyreferred to as refrigerant 12.'Refrigerant 12 has a boiling point atatmospheric pressure of about -2 1 .6 F. The charge level in manyGeneral Motors automobile air conditioning systems is approximately 4lbs. of refrigerant. It has been observed that a charge of less thanabout 1 lb. of refrigerant may result in insufficient cooling andlubrication of the compressor. 7

When the refrigerant-charge level is insufficient for cooling andlubricating the compressor, the superheat temperature of refrigerant inthe compressor inlet or suction cavity 94 is significantly increased.Undernormal operation with a full refrigerant charge'and a heat load onthe evaporator, the throttling valve 20 of the air conditioning systemrestricts refrigerant flow in the suction line to maintain a refrigerantpressure of about 30 psig which corresponds to a refrigerant temperatureof 32 F. in the evaporator. If the vapor in the suction cavity is at 40F. at 30 psig, its superheat is about 8 F.

When a relatively large heat load is placed on the evaporator, withareduced refrigerant charge on one pound, the superheat of refrigerantin the compressors inlet or suction cavity may exceed F. This maycorrespond to a refrigerant temperature of F. at about 30 psig or alesser temperature of 120 F. at near zero psig. With a 4 poundrefrigerant charge under the same conditions, a relatively low-superheattemperatore of 10 15 F. would normally be expected which corresponds toabout 32 F. at 30 psig. The contacts 96, 120 may be calibrated todesirably close at a superheat of about 141 F. corresponding to arefrigerant temperature of 120 F. at zero psig.

When the heat load on the evaporator decreases by operation of thesystem under low ambient temperature conditions with only a 1 poundrefrigerant charge, the superheat in the compressor inlet may fall toonly 45 F. This normally would be insufficient to close, contacts 96,120. However, under these conditions, the throttling valve 20 maycompletely shut off refrigerant flow to the compressor and a negativepressure condition will occur in the suction cavity. The combination oftemperature and unusually low pressure will cause casing l06to expandand engage contacts 96, 120 to terminate. compressor operation. Thus,the pressure responsive characteristics of the refrigerant responsiveportion of switch assembly 44 assume importance under. low ambienttemperature operation of the system.-

Operation of the air conditioning system under some conditions with afull refrigerant charge may temporarily produce predetermined closingpoint of contacts 96, 120. For example, this can occur during rapidacceleration of the automobile or after'consecutive stopping andstarting of the compressor. The present refrigerant responsive switchportion of assembly 44 is insensitive to these transient temperature andpressure conditions. The thermistor 104 requires a brief period tobecome fully conductive after the contacts 96 and 120 engage andconsequently blow fuse 38. After this delay, the opening of fuse 38de-energizes thecompressor 10.

superheats which exceed the Once the fuse 38 is blown and the circuit tothe coil 32 is broken, the fuse must be replaced in order to once againenergize the clutch of the compressor. Normally, replacement of the fuseis done by professional service which at the same time checks andreplenishes the refrigerant charge. However, if the refrigerant chargeis not replenished, and the fuse replaced, the system will not bedamaged since the new fuse will be blown in the same manner as describedabove.

While the embodiment of the invention described above is a preferredembodiment, it should be understood that other embodiments may beadapted.

What is claimed is as follows:

1. A combination ambient air temperature and refrigerant temperature andpressure control for an automobile air conditioning system comprising: acompressor having an inlet; clutch means including an electricallyresponsive coil for transmitting power from the automobile engine tosaid compressor when the clutch coil is energized; a coil energizationcircuit including a battery and a fuse; ambient air temperatureresponsive switch means in said energization circuit which operatesabove a predetermined ambient air temperature to energize said coil; arefrigerant temperature and pressure responsive switch having a thermalbulb and a pressure responsive casing in fluid contact with refrigerantin the inlet of said compressor; said temperature and pressureresponsive switch having a pair of contacts controlled by said casingadapted to close in response to predetermined refrigerant temperaturesand pressures; means including said refrigerant responsive switch and athermistor defining a ground circuit from said fuse in shuntrelationship to said clutch coil; said thermistor having an initial highresistance upon closure of said pair of contacts to delay shortcircuiting of said fuse whereby transient high temperatures and lowpressures of refrigerant will not deactivate said clutch coil; saidthermistor having a reduced resistance following the delay to cause alarge current to pass through said fuse to cause it to blow.

2/ A combination ambient air temperature and refrigerant temperature andpressure control for an automobile air conditioning system comprising: acornpressor having an inlet; clutch means including an electricallyresponsive coil for transmitting power from the automobile engine tosaid compressor when said coil is energized; a coil energization circuithaving a battery and a fuse; an ambient air temperature responsiveswitch in said energization circuit which operates above a predeterminedambient air temperature to energize said coil; a refrigerant temperatureand pressure responsive switch in fluid contact with refrigerant.

in the inlet of said compressor adapted to close in response topredetermined refrigerant temperatures and pressures; said switcheshaving circular discs in spaced relation to one another with theirperipheral edges joined and with the space therebetween filled withrefrigerant; one of each pair of spaced discs being fixedly supported bya switch housing; movable contacts on the other of each pair of spaceddiscs; fixed contacts supported by said switch housing in spacedrelation to said movable contacts when said switches are open; meansincluding said refrigerant responsive switch and a thermistor in circuitwith said battery and said fuse to bypass the clutch coil and shortcircuit said fuse when said contacts of said refrigerant responsiveswitch are closed; said thermistor operating to delay short circuitingof said fuse whereby temporary increases in refrigerant temperature andtemporary decreases in refrigerant pressure will not de-energize saidcompressor.

1. A combination ambient air temperature and refrigerant temperature andpressure control for an automobile air conditioning system comprising: acompressor having an inlet; clutch means including an electricallyresponsive coil for transmitting power from the automobile engine tosaid compressor When the clutch coil is energized; a coil energizationcircuit including a battery and a fuse; ambient air temperatureresponsive switch means in said energization circuit which operatesabove a predetermined ambient air temperature to energize said coil; arefrigerant temperature and pressure responsive switch having a thermalbulb and a pressure responsive casing in fluid contact with refrigerantin the inlet of said compressor; said temperature and pressureresponsive switch having a pair of contacts controlled by said casingadapted to close in response to predetermined refrigerant temperaturesand pressures; means including said refrigerant responsive switch and athermistor defining a ground circuit from said fuse in shuntrelationship to said clutch coil; said thermistor having an initial highresistance upon closure of said pair of contacts to delay shortcircuiting of said fuse whereby transient high temperatures and lowpressures of refrigerant will not deactivate said clutch coil; saidthermistor having a reduced resistance following the delay to cause alarge current to pass through said fuse to cause it to blow.
 2. Acombination ambient air temperature and refrigerant temperature andpressure control for an automobile air conditioning system comprising: acompressor having an inlet; clutch means including an electricallyresponsive coil for transmitting power from the automobile engine tosaid compressor when said coil is energized; a coil energization circuithaving a battery and a fuse; an ambient air temperature responsiveswitch in said energization circuit which operates above a predeterminedambient air temperature to energize said coil; a refrigerant temperatureand pressure responsive switch in fluid contact with refrigerant in theinlet of said compressor adapted to close in response to predeterminedrefrigerant temperatures and pressures; said switches having circulardiscs in spaced relation to one another with their peripheral edgesjoined and with the space therebetween filled with refrigerant; one ofeach pair of spaced discs being fixedly supported by a switch housing;movable contacts on the other of each pair of spaced discs; fixedcontacts supported by said switch housing in spaced relation to saidmovable contacts when said switches are open; means including saidrefrigerant responsive switch and a thermistor in circuit with saidbattery and said fuse to bypass the clutch coil and short circuit saidfuse when said contacts of said refrigerant responsive switch areclosed; said thermistor operating to delay short circuiting of said fusewhereby temporary increases in refrigerant temperature and temporarydecreases in refrigerant pressure will not de-energize said compressor.